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You searched for: creator:"L. L. Salcedo"
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[texts]On the uniqueness of the expected stress-energy tensor in renormalizable field theories - L. L. Salcedo
It is argued that the ambiguity introduced by the renormalization in the effective action of a four-dimensional renormalizable quantum field theory is at most a local polynomial action of canonical dimension four. The allowed ambiguity in the expected stress-energy tensor of a massive scalar field is severely restricted by this fact.
Downloads: 3
[texts]Comment on "Quantum back-reaction through the Bohmian particle" - L. L. Salcedo
In this Comment I point out some limitations of the proposal of Prezhdo and Brooksby for coupling quantum and classical degrees of freedom (Phys.Rev.Lett.86(2001)3215) if it is pushed too far.
Downloads: 3
[texts]The invariant factor of the chiral determinant - L. L. Salcedo
The coupling of spin 0 and spin 1 external fields to Dirac fermions defines a theory which displays gauge chiral symmetry. Quantum mechanically, functional integration of the fermions yields the determinant of the Dirac operator, known as the chiral determinant. Its modulus is chiral invariant but not so its phase, which carries the chiral anomaly through the Wess-Zumino-Witten term. Here we find the remarkable result that, upon removal from the chiral determinant of this known anomalous part, t...
Downloads: 3
[texts]Absence of classical and quantum mixing - L. L. Salcedo
It is shown, under mild assumptions, that classical degrees of freedom dynamically coupled to quantum ones do not inherit their quantum fluctuations. It is further shown that, if the assumptions are strengthen by imposing the existence of a canonical structure, only purely classical or purely quantum dynamics are allowed.
Downloads: 4
[texts]Derivative expansion for the effective action of chiral gauge fermions. The abnormal parity component - L. L. Salcedo
Explicit exact formulas are presented, for the leading order term in a strict chiral covariant derivative expansion, for the abnormal parity component of the effective action of two- and four-dimensional Dirac fermions in presence of scalar, pseudo-scalar, vector and axial vector background fields. The formulas hold for completely general internal symmetry groups and general configurations. In particular the scalar and pseudo-scalar fields need not be on the chiral circle.
Downloads: 3
[texts]Derivative expansion for the effective action of chiral gauge fermions. The normal parity component - L. L. Salcedo
Explicit exact formulas are presented, up to fourth order in a strict chiral covariant derivative expansion, for the normal parity component of the Euclidean effective action of even-dimensional Dirac fermions. The bosonic background fields considered are scalar, pseudo-scalar, vector and axial vector. No assumptions are made on the internal symmetry group and, in particular, the scalar and pseudo-scalar fields need not be on the chiral circle.
Downloads: 2
[texts]Derivative expansion of the heat kernel in curved space - L. L. Salcedo
The heat kernel in curved space-time is computed to fourth order in a strict expansion in the number of covariant derivatives. The computation is made for arbitrary non abelian gauge and scalar fields and for the Riemann connection in the coordinate sector. The expressions obtained hold for arbitrary tensor representations of the matter field. Complete results are presented for the diagonal matrix elements and for the trace of the heat kernel operator...
Downloads: 12
[texts]Temperature dependence of the anomalous effective action of fermions in two and four dimensions - L. L. Salcedo
The temperature dependence of the anomalous sector of the effective action of fermions coupled to external gauge and pseudo-scalar fields is computed at leading order in an expansion in the number of Lorentz indices in two and four dimensions. The calculation preserves chiral symmetry and confirms that a temperature dependence is compatible with axial anomaly saturation. The result checks soft-pions theorems at zero temperature as well as recent results in the literature for the pionic decay amp...
Downloads: 3
[texts]Existence of positive representations for complex weights - L. L. Salcedo
The necessity of computing integrals with complex weights over manifolds with a large number of dimensions, e.g., in some field theoretical settings, poses a problem for the use of Monte Carlo techniques. Here it is shown that very general complex weight functions P(x) on R^d can be represented by real and positive weights p(z) on C^d, in the sense that for any observable f, _P = _p, f(z) being the analytical extension of f(x)...
Downloads: 4
[texts]Parity breaking in 2+1 dimensions and finite temperature - L. L. Salcedo
An expansion in the number of spatial covariant derivatives is carried out to compute the $\zeta$-function regularized effective action of 2+1-dimensional fermions at finite temperature in an arbitrary non-Abelian background. The real and imaginary parts of the Euclidean effective action are computed up to terms which are ultraviolet finite. The expansion used preserves gauge and parity symmetries and the correct multivaluation under large gauge transformations as well as the correct parity anom...
Downloads: 3
[texts]On the cascade approach to the quantum multiscattering problem - L. L. Salcedo
The multiscattering problem is studied in the matrix density formalism. We study how to isolate the quasi-classical degrees of freedom in order to connect with a cascade approach. The different problems that arise, as well as their possible solutions, are discussed and exemplified with a pion-nucleus model.
Downloads: 3
[texts]Representation of Complex Probabilities - L. L. Salcedo
Let a ``complex probability'' be a normalizable complex distribution $P(x)$ defined on $\R^D$. A real and positive probability distribution $p(z)$, defined on the complex plane $\C^D$, is said to be a positive representation of $P(x)$ if $\langle Q(x)\rangle_P = \langle Q(z)\rangle_p$, where $Q(x)$ is any polynomial in $\R^D$ and $Q(z)$ its analytical extension on $\C^D$. In this paper it is shown that every complex probability admits a real representation and a constructive method is given...
Downloads: 3
[texts]Comment on ``A quantum-classical bracket that satisfies the Jacobi identity'' [J. Chem. Phys. 124, 201104 (2006)] - L. L. Salcedo
It shown that the quantum-classical dynamical bracket recently proposed in J. Chem. Phys. 124, 201104 (2006) fails to satisfy the Jacobi identity.
Downloads: 5
[texts]Direct construction of the effective action of chiral gauge fermions in the anomalous sector - L. L. Salcedo
The anomaly implies an obstruction to a fully chiral covariant calculation of the effective action in the abnormal parity sector of chiral theories. The standard approach then is to reconstruct the anomalous effective action from its covariant current. In this work we use a recently introduced formulation which allows to directly construct the non trivial chiral invariant part of the effective action within a fully covariant formalism...
Downloads: 27
[texts]Leading order one-loop CP and P violating effective action in the Standard Model - L. L. Salcedo
The fermions of the Standard Model are integrated out to obtain the effective Lagrangian in the sector violating P and CP at zero temperature. We confirm that no contributions arise for operators of dimension six or less and show that the leading operators are of dimension eight. To assert this we explicitly compute one such non-vanishing contribution, namely, that with three Z^0, two W^+ and two W^-...
Downloads: 10
[texts]The method of covariant symbols in curved space-time - L. L. Salcedo
Diagonal matrix elements of pseudodifferential operators are needed in order to compute effective Lagrangians and currents. For this purpose the method of symbols is often used, which however lacks manifest covariance. In this work the method of covariant symbols, introduced by Pletnev and Banin, is extended to curved space-time with arbitrary gauge and coordinate connections. For the Riemannian connection we compute the covariant symbols corresponding to external fields, the covariant derivativ...
Downloads: 10
[texts]The induced Chern-Simons term at finite temperature - L. L. Salcedo
It is argued that the derivative expansion is a suitable method to deal with finite temperature field theory, if it is restricted to spatial derivatives only. Using this method, a simple and direct calculation is presented for the radiatively induced Chern-Simons--like piece of the effective action of (2+1)-dimensional fermions at finite temperature coupled to external gauge fields. The gauge fields are not assumed to be subjected to special constraints, and in particular, they are not required ...
Downloads: 8
[texts]Statistical consistency of quantum-classical hybrids - L. L. Salcedo
After formulating a no-go theorem for perfect quantum-classical hybrid systems, a new consistency requirement based on standard statistical considerations is noted. It is shown that such requirement is not fulfilled by the mean-field approach, nor by the statistical ensemble approach. Further unusual features of the latter scheme are pointed out.
Downloads: 10
[texts]Covariant derivative expansion of the heat kernel - L. L. Salcedo
Using the technique of labeled operators, compact explicit expressions are given for all traced heat kernel coefficients containing zero, two, four and six covariant derivatives, and for diagonal coefficients with zero, two and four derivatives. The results apply to boundaryless flat space-times and arbitrary non Abelian scalar and gauge background fields.
Downloads: 15
[texts]Renormalizability of semiquantized fields - L. L. Salcedo
A definition is given, in the framework of stochastic quantization, for the dynamics of a system composed of classical and quantum degrees of freedom mutually interacting. It is found that the theory breaks reflection positivity, and hence it is unphysical. The Feynman rules for the Euclidean vacuum expectation values are derived and the perturbative renormalizability of the theory is analyzed. Contrary to the naive expectation, the semiquantized theory turns out to be less renormalizable, in ge...
Downloads: 4
[texts]Generalized heat kernel coefficients - L. L. Salcedo
Following Osipov and Hiller, a generalized heat kernel expansion is considered for the effective action of bosonic operators. In this generalization, the standard heat kernel expansion, which counts inverse powers of a c-number mass parameter, is extended by allowing the mass to be a matrix in flavor space. We show that the generalized heat kernel coefficients can be related to the standard ones in a simple way...
Downloads: 68
[texts]Impediments to mixing classical and quantum dynamics - J. Caro
The dynamics of systems composed of a classical sector plus a quantum sector is studied. We show that, even in the simplest cases, (i) the existence of a consistent canonical description for such mixed systems is incompatible with very basic requirements related to the time evolution of the two sectors when they are decoupled. (ii) The classical sector cannot inherit quantum fluctuations from the quantum sector...
Downloads: 1
[texts]SU(6)$\supset$SU(3)xSU(2) and SU(8)$\supset$SU(4)xSU(2) Clebsch-Gordan coefficients - C. Garcia-Recio
Tables of scalar factors are presented for 63x63 and 120x63 in SU(8)$\supset$SU(4)xSU(2), and for 35x35 and 56x35 in SU(6)$\supset$SU(3)xSU(2). Related tables for SU(4)$\supset$SU(3)xU(1) and SU(3)$\supset$SU(2)xU(1) are also provided so that the Clebsch-Gordan coefficients can be completely reconstructed. These are suitable to study meson-meson and baryon-meson within a spin-flavor symmetric scheme.
Downloads: 2
[texts]CP violation in the effective action of the Standard Model - C. Garcia-Recio
Following a suggestion by Smit, the CP odd terms of the effective action of the Standard Model, obtained by integration of quarks and leptons, are computed to sixth order within a strict covariant derivative expansion approach. No other approximations are made. The final result so derived includes all Standard Model gauge fields and Higgs. Remarkably, at the order considered in this work, all parity violating contributions turn out to be zero...
Downloads: 9
[texts]Chiral anomaly and nucleon properties in the Nambu--Jona-Lasinio model with vector mesons - E. Ruiz Arriola
We consider the extended SU(3) Nambu and Jona-Lasinio model with explicit vector couplings in the presence of external fields. We study the chiral anomaly in this model and its implications on the properties of the nucleon described as a chiral soliton of three valence quarks bounded in mesonic background fields. For the model to reproduce the QCD anomaly it is necessary to subtract suitable local and polynomial counterterms in the external and dynamical vector and axial-vector fields...
Downloads: 9
[texts]New Improvements for Mie Scattering Calculations - V. E. Cachorro
New improvements to compute Mie scattering quantities are presented. They are based on a detailed analysis of the various sources of error in Mie computations and on mathematical justifications. The algorithm developed on these improvements proves to be reliable and efficient, without size ($x=2\pi R/\lambda$) nor refractive index ($m=m_R-{\rm i}m_I$) limitations, and the user has a choice to fix in advance the desired precision in the results...
Downloads: 7
[texts]Gauge invariant derivative expansion of the effective action at finite temperature and density and the scalar field in 2+1 dimensions - C. García-Recio
A method is presented for the computation of the one-loop effective action at finite temperature and density. The method is based on an expansion in the number of spatial covariant derivatives. It applies to general background field configurations with arbitrary internal symmetry group and space-time dependence. Full invariance under small and large gauge transformations is preserved without assuming stationary or Abelian fields nor fixing the gauge...
Downloads: 19
[texts]Chiral and scale anomalies of non local Dirac operators - E. Ruiz Arriola
The chiral and scale anomalies of a very general class of non local Dirac operators are computed using the $\zeta$-function definition of the fermionic determinant. For the axial anomaly all new terms introduced by the non locality are shown to be removable by counterterms and such counterterms are also explicitly computed. It is verified that the non local Dirac operators have the standard minimal anomaly in Bardeen's form.
Downloads: 2
[texts]Derivative expansion of the heat kernel at finite temperature - F. J. Moral-Gamez
The method of covariant symbols of Pletnev and Banin is extended to space-times with topology $\R^n\times S^1\times ... \times S^1$. By means of this tool, we obtain explicit formulas for the diagonal matrix elements and the trace of the heat kernel at finite temperature to fourth order in a strict covariant derivative expansion. The role of the Polyakov loop is emphasized. Chan's formula for the effective action to one loop is similarly extended...
Downloads: 7
[texts]The perturbative scalar massless propagator in Schwarzschild spacetime - C. Garcia-Recio
A short derivation is given of the weak gravitational field approximation to the scalar massless propagator in Schwarzschild spacetime obtained by Paszko using the path-integral approach. The contribution from the direct coupling of the quantum field to the scalar curvature is explictly included. The propagator complies with Hadamard's pattern, and the vacuum state is consistent with the perturbative version of the Boulware vacuum...
Downloads: 11
[texts]Anomalies for Nonlocal Dirac Operators - E. Ruiz Arriola
The anomalies of a very general class of non local Dirac operators are computed using the $\zeta$-function definition of the fermionic determinant and an asymmetric version of the Wigner transformation. For the axial anomaly all new terms introduced by the non locality can be brought to the standard minimal Bardeen's form. Some extensions of the present techniques are also commented.
Downloads: 11
[texts]Wigner transformation for the determinant of Dirac operators - L. L. Salcedo
We use the $\zeta$-function regularization and an integral representation of the complex power of a pseudo differential operator, to give an unambiguous definition of the determinant of the Dirac operator. We bring this definition to a workable form by making use of an asymmetric Wigner representation. The expression so obtained is amenable to several treatments of which we consider in detail two, the inverse mass expansion and the gradient expansion, with concrete examples...
Downloads: 19
[texts]Polyakov loop at low and high temperatures - E. Megias
We describe how the coupling of the gluonic Polyakov loop to quarks solves different inconsistencies in the standard treatment of chiral quark models at finite temperature at the one quark loop level. Large gauge invariance is incorporated and an effective theory of quarks and Polyakov loops as basic degrees of freedom is generated. From this analysis we find a strong suppression of finite temperature effects in hadronic observables below the deconfinement phase transition triggered by approxima...
Downloads: 3
[texts]Low Energy Chiral Lagrangian in Curved Space-Time from the Spectral Quark Model - E. Megias
We analyze the recently proposed Spectral Quark Model in the light of Chiral Perturbation Theory in curved space-time. In particular, we calculate the chiral coefficients $L_1, ..., L_{10}$, as well as the coefficients $L_{11}$, $L_{12}$, and $L_{13}$, appearing when the model is coupled to gravity. The analysis is carried for the SU(3) case. We analyze the pattern of chiral symmetry breaking as well as elaborate on the fulfillment of anomalies...
Downloads: 3
[texts]From Chiral quark dynamics with Polyakov loop to the hadron resonance gas model - E. Ruiz Arriola
Chiral quark models with Polyakov loop at finite temperature have been often used to describe the phase transition. We show how the transition to a hadron resonance gas is realized based on the quantum and local nature of the Polyakov loop.
Downloads: 7
[texts]Semiclassical expansions up to $\hbar^4$-order in relativistic nuclear physics - J. Caro
We present the first calculation of the $\hbar^4$-Wigner--Kirkwood corrections to a relativistic system of fermions in the presence of external scalar and vector potentials. The method we propose allows to compute efficiently semiclassical corrections to one body operators such as mean energies and local densities. It also preserves gauge invariance and produces explicitly convergent results despite some apparent divergencies at the classical turning points...
Downloads: 5
[texts]Elimination of the vacuum instability for finite nuclei in the relativistic $σ$-$ω$ model - J. Caro
The $\sigma$-$\omega$ model of nuclei is studied at leading order in the $1/N$ expansion thereby introducing the self consistent Hartree approximation, the Dirac sea corrections and the one fermion loop meson self energies in a unified way. For simplicity, the Dirac sea is further treated within a semiclassical expansion to all orders. The well-known Landau pole vacuum instability appearing in this kind of theories is removed by means of a scheme recently proposed in this context...
Downloads: 4
[texts]The quark-antiquark potential at finite temperature and the dimension two gluon condensate - E. Megias
A recently proposed phenomenological model, which includes non perturbative effects from dimension two gluon condensates, is applied to analyze the available lattice data for the heavy quark free energy in the deconfined phase of quenched QCD. For large $q\bar{q}$ separations we recover previous results for the Polyakov loop, exhibiting unequivocal condensate contributions. For the $q\bar{q}$ potential at finite temperature and finite separation we find that a good overall description of the lat...
Downloads: 4
[texts]The hadron resonance gas model: thermodynamics of QCD and Polyakov loop - E. Megias
We study the hadron resonance gas model and describe the equation of state of QCD and the vacuum expectation value of the Polyakov loop in the confined phase, in terms of hadronic states with light quarks in the first case, and with exactly one heavy quark in the second case. Comparison with lattice simulations is made.
Downloads: 6
[texts]Chiral Lagrangian at finite temperature from the Polyakov-Chiral Quark Model - E. Megias
We analyze the consequences of the inclusion of the gluonic Polyakov loop in chiral quark models at finite temperature. Specifically, the low-energy effective chiral Lagrangian from two such quark models is computed. The tree level vacuum energy density, quark condensate, pion decay constant and Gasser-Leutwyler coefficients are found to acquire a temperature dependence. This dependence is, however, exponentially small for temperatures below the mass gap in the full unquenched calculation...
Downloads: 2
[texts]Feynman diagrams with the effective action - M. J. de la Plata
A derivation is given of the Feynman rules to be used in the perturbative computation of the Green's functions of a generic quantum many-body theory when the action which is being perturbed is not necessarily quadratic. Some applications are discussed.
Downloads: 4
[texts]The thermal heat kernel expansion and the one-loop effective action of QCD at finite temperature - E. Megias
The heat kernel expansion for field theory at finite temperature is constructed. It is based on the imaginary time formalism and applies to generic Klein-Gordon operators in flat space-time. Full gauge invariance is manifest at each order of the expansion and the Polyakov loop plays an important role at any temperature. The expansion is explicitly worked out up to operators of dimension six included...
Downloads: 4
[texts]D^- mesic atoms - C. Garcia-Recio
The anti-D meson self-energy is evaluated self-consistently, using unitarized coupled-channel theory, by computing the in-medium meson-baryon T-matrix in the C=-1,S=0 sector. The heavy pseudo-scalar and heavy vector mesons, anti-D and anti-D^*, are treated on equal footing as required by heavy quark spin symmetry. Results for energy levels and widths of D^- mesic atoms in 12C, 40Ca, 118Sn and 208Pb are presented...
Downloads: 4
[texts]Resonances and the Weinberg--Tomozawa 56-baryon --35-meson interaction - C. Garcia-Recio
Vector meson degrees of freedom are incorporated into the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian by using a scheme which relies on spin--flavor SU(6) symmetry. The corresponding Bethe-Salpeter approximation successfully reproduces previous SU(3)--flavor WT results for the lowest-lying s--wave negative parity baryon resonances, and it also provides some information on the dynamics of the heavier ones...
Downloads: 2
[texts]Semiclassical treatment of the Dirac sea contribution for finite nuclei - J. Caro
Dirac sea corrections for bulk properties of finite nuclei are computed within a self-consistent scheme in the $\sigma$-$\omega$ model. The valence part is treated in the Hartree approximation whereas the sea contribution is evaluated semiclassically up to fourth order in $\hbar$. Numerically, we find a quick convergence of the semiclassical expansion; the fourth order contributing much less than one percent to the binding energy per nucleon.
Downloads: 3
[texts]Dimension two condensates and the Polyakov loop above the deconfinement phase transition - E. Megias
We show that recent available lattice data for the renormalized Polyakov loop above the deconfinement phase transition exhibit unequivocal inverse power temperature corrections driven by a dimension 2 gluon condensate. This simple ansatz provides a good overall description of the data throughout the deconfinement phase until near the critical temperature with just two parameters. One of the parameters is consistent with perturbation theory while a second, non perturbative, parameter provides a n...
Downloads: 2
[texts]The Quantum and Local Polyakov loop in Chiral Quark Models at Finite Temperature - E. Megias
We describe results for the confinement-deconfinement phase transition as predicted by the Nambu--Jona-Lasinio model where the local and quantum Polyakov loop is coupled to the constituent quarks in a minimal way (PNJL). We observe that the leading correlation of two Polyakov loops describes the chiral transition accurately. The effects of the current quark mass on the transition are also analysed.
Downloads: 5
[texts]Meson-Baryon s-wave Resonances with Strangeness -3 - C. Garcia-Recio
Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian (Phys. Rev. D74 (2006) 034025), we study the s-wave meson-baryon resonances in the strangeness S=-3 and negative parity sector. Those resonances are generated by solving the Bethe-Salpeter equation with the WT interaction used as kernel. The considered mesons are those of the 35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the vector (V) nonet of the rho meson...
Downloads: 6
[texts]Short range correlations in the pion s-wave self-energy of pionic atoms - L. L. Salcedo
We evaluate the contribution of second order terms to the pion-nucleus s-wave optical potential of pionic atoms generated by short range nuclear correlation. The corrections are sizeable because they involve the isoscalar s-wave $\pi N$ amplitude for half off-shell situations where the amplitude is considerably larger than the on-shell one. In addition, the s-wave optical potential is reanalyzed by looking at all the different conventional contributions together lowest order, Pauli corrected res...
Downloads: 6
[texts]Trace Anomaly, Thermal Power Corrections and Dimension Two condensates in the deconfined phase - E. Megias
The trace anomaly of gluodynamics on the lattice shows clear fingerprints of a dimension two condensate above the phase transition. The condensate manifests itself through even powers of the inverse temperature while the total perturbative contribution corresponds to a mild temperature dependence and turns out to be compatible with zero within errors. We try several resummation methods based on a renormalization group improvement...
Downloads: 8
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